Hi all, I'm looking into the rewriting pipeline, specifically for HTTP responses, with a few goals in mind: 1. Consolidate ImageRewriter with RequestRewriter, so it's not just a one-off rewriter injection. - And to simplify the rewriter interfaces overall, to allow for uniform rewriter profiling code etc. 2. Expand RequestRewriters' capability to modify HTTP response headers. 3. Maintain - and expand - our ability to cache the result of rewriting passes intelligently. Especially important for ImageRewriter, the output of which is presently cached for notable performance gains.
To this end, I've created the following CL as a starting point. It builds upon the CL I recently submitted adding the ability to manipulate MutableContent by byte-array: http://codereview.appspot.com/1032042/show Downstream of this CL, I'm proposing to change the rewriter interface roughly as follows: OLD // Return true if content modified. boolean RequestRewriter.rewrite(HttpRequest, HttpResponse, MutableContent); NEW // Return value represents caching behavior. // Naive strategy: return boolean. True = HttpRequest is a sufficient key to cache the rewrite. Works for simple cases, but compound rewriter cases may be more difficult. // More sophisticated implementation: return a RewriteCacheKey object, containing a normalized set of all inputs to the rewrite behavior (essentially a compound key). // In turn, these objects would be used by a RewriterCache manager responsible for managing these states. ??? ResponseRewriter.rewrite(HttpRequest, HttpResponseBuilder); Note that I suggest a new interface: ResponseRewriter (a more accurate name for RequestRewriter anyway), so we can support both Request and ResponseRewriter implementations during transition. Alternate approaches: I also considered simply splitting out the HTTP header-manipulation methods from HttpResponseBuilder into an interface: HttpResponseHeaders. RequestRewriter's API would be modified simply as: boolean RequestRewriter.rewrite(HttpRequest, HttpResponseHeaders, MutableContent); While simpler, this had the downsides: * Still involves a signature change. * Doesn't account for better caching behavior. * Involves 2 objects rather than 1 to manipulate for output. At present, I'd like to go the conservative route: 1. HttpResponseBuilder as MutableContent (@see CL) 2. Introduce ResponseRewriter interface, returning RewriteCacheKey with simple flags: HttpRequest-is-sufficient and rewrite-is-idempotent. 3. Transition ImageRewriter to ResponseRewriter. 4. Transition RequestRewriters to ResponseRewriter interface. Thoughts? Input welcome. Cheers, John
